Add script for testing reading and writing files.

SwiftShellTests/Scripts/readandwritefiles.swift

@@ -0,0 +1,32 @@
+#!/usr/bin/env swiftshell
+
+import SwiftShell
+
+let filepath = tempdirectory.URLByAppendingPathComponent("newfile.txt").path!
+
+// File doesn't exist. Create it.
+let file1 = open(forWriting: filepath )
+file1.writeln("line 1")
+file1.closeStream()
+
+// File does exist. Append it.
+let file2 = open(forWriting: filepath)
+file2.writeln("line 2")
+file2.closeStream()
+
+// Test file.
+let file3 = open(filepath)
+if file3.read() != "line 1\nline 2\n" {
+	printErrorAndExit( "newfile.txt should contain 'line 1\\n line 2\\n'." )
+}
+
+// File exists. Overwrite it.
+let file4 = open(forWriting: filepath, overwrite: true)
+file4.write("file now contains only this")
+file4.closeStream()
+
+// Test file.
+let file5 = open(filepath)
+if file5.read() != "file now contains only this" {
+	printErrorAndExit( "newfile.txt should contain 'file now contains only this'." )
+}

SwiftShellTests/Scripts/testall.bash

@@ -14,3 +14,4 @@ ls | ./print_linenumbers.swift
 ./readfilelinebyline.swift
 ./stream_out.swift
 ./callswiftscriptfromswift.swift
+./readandwritefiles.swift